Present techniques intended to prevent successful counterfeiting of, say, banknotes include the use of intricate designs, watermarks and inlaid linear metallized plastic strips, the intention being that the application of these devices to banknote paper is sufficiently difficult to make it likely that forged notes will be readily recognisable by their poor quality. However, the effectiveness of such preventive measures is continuously being eroded as the techniques and apparatus available to the forger become more advanced and easier to operate, thus making it potentially easier to simulate the present form of banknotes.
It is therefore desirable that the production of the security device, and/or its application to the document concerned should involve the use of devices or resources which, by reason of their nature, complexity, cost or other factors would not normally be available to the forger and would be difficult to imitate successfully. Further it should preferably be readily possible to test the document to establish its authenticity.